Curable acrylate polymer compositions featuring improved flexural characteristics

ABSTRACT

The invention describes acrylic and methacrylic acid ester-based polymeric materials containing as flexibilizing and brittleness reducing agents 1-60% of C 4 -C 8  polyalkylene or polyalkyldiene compounds, preferably having a molecular weight of 300-2100, and the use of such materials in dentistry and medicine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to modified, acrylate polymer compositionsfeaturing reduced brittleness, such polymers being particularly suitableas dental/medical cements and restorative materials and formanufacturing dental prosthetics.

2. Description of the Related Art

Polymeric materials based on the esters of methacrylic acid have foundwidespread industrial and medical applications. Their role isparticularly prominent in dentistry where they have become a base formodern restorative materials, cements, varnishes, cavity liners andsealers. In medicine perhaps the most important uses of acrylic resinsinclude contact lenses and cements used for hip restorations.

Many of these applications require the material to meet a combination ofrequirements with respect to their chemical, optical and mechanicalproperties and, frequently, biological compatibility. While acrylicresins, due to a variety of available monomers, usually make it possibleto compound a blend which, upon cure, will result in a polymer meetingthe requirements of tissue biocompatibility, wear resistance,translucency, mechanical strength or hardness, they frequently fail orare less than satisfactory in applications requiring flexibility. It isespecially true in situations where thin layers of polymers are exposedto flexural forces; for example, while placing or removing a well-fitteddevice. Another example of situations where the greater flexibility andimpact resistance of acrylic polymers would be highly desirable areapplications where the devices made of such polymeric materials areexposed to rapid or repetitiously applied forces. Especially vulnerableare thin areas of such objects.

In applications requiring longevity, mechanical strength and resistanceto exposure to environments which may have a deteriorating effect on thepolymeric material by means of wear, chemical reaction, exposure toheat, light, etc., cross-linked acrylic polymers are generally preferredover the linear ones. Consequently, in addition to monounsaturatedmonomers frequently used in such applications, exemplified byalkylmethacrylates, tetrahydrofurfuryl methacrylate and hydroxyalkylmethacrylates, di-, tri- or even higher polymethacrylates are employed.Such polyfunctional monomers may be used in blends with monofunctionalsserving as cross-linking agents, or in compositions where monofunctionalmonomers are absent. In applications requiring high mechanical strengthand chemical and wear resistance, in addition to low polymerizationshrinkage and low exotherm of the curing process, higher molecularweight dimethacrylates are generally the monomers of choice. Suchmonomers are particularly useful in formulating modern self- andlight-cured dental restorative materials, prostheses, cements, cavityliners, varnishes and sealers. Their use is also expanding in orthopedicsurgery, where they are replacing, or being used as adjuncts to,monomethacrylate monomers to enhance mechanical properties and chemicalresistance of resulting polymers.

Acrylic resins have unique features making them difficult to replacewith other types of monomers, especially in particular or very demandingapplications. These include ease of control of working and curing times,good biocompatibility, and a broad selection of available monomers, andrelative ease of synthesizing new ones, having desirable molecularstructures allows for modifying or controlling relevant characteristicsof cured polymers such as water absorption, solubility, hydrophobicity,adhesive properties, compatibility with various additives, opticalproperties, mechanical strength, chemical resistance and resistance toheat and UV light. These properties allow for multiple ways of inducingpolymerization, such as by chemical means, heat, or light.

These advantages make acrylic resin unique, important and oftenirreplaceable in many applications, especially in a dental field thathas been revolutionized by their advent and consequent expansion.

SUMMARY OF THE INVENTION

Compositions according to preferred embodiments, in which olefinicpolymers are used as additives to acrylic polymers, provide moreflexible and impact-resistant acrylate polymers suitable for a varietyof uses, particularly those related to medical and dental fields.Preferred compositions also effectively address the reducing oreliminating of the oxygen-inhibited layer and/or reducing the exothermiceffect of the polymerization process.

Another advantage of polymers in accordance with preferred embodiments,particularly important in medical and dental applications, is theirgeneral lack of toxicity as well as a low incidence or absence ofallergenic reaction and tissue irritation.

In accordance with preferred embodiments, there is provided a curablecomposition comprising about 10-90% by weight of one or more acrylicmonomers; and about 1-60% by weight of an olefinic component comprisingoligomers or polymers of one or more straight chain or branched C4-C6monomers having one or two double bonds per monomer molecule. Thecompositions may further comprise one or more additives selected fromthe group consisting of polymerization initiators, polymerizationactivators, stabilizers, UV light absorbers, colorants, fillers,therapeutic agents, flavoring agents and viscosity/rheologicalmodifiers. The compositions may exist as one part or component, or theymay be in two parts that are mixed together prior to use. Thecomposition may be used in medical and/or dental applications as amedical device such as a restorative material, prosthesis, cement,cavity liner, varnish or sealer.

In accordance with one embodiment, there is provided a method ofperforming a dental procedure, comprising obtaining a curablecomposition comprising 10-90% by weight of one or more acrylic monomersand 1-60% by weight of an olefinic component comprising oligomers orpolymers of one or more straight chain or branched C4-C6 monomers havingone or two double bonds per monomer molecule; applying the compositionto at least one surface of a tooth or dental appliance; and allowing thecomposition to cure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The technology disclosed herein relates to heat, chemically (i.e.self-curable) or light (UV and/or visible) curable acrylate acrylicresin-based formulations as well as polymers or objects resulting fromcuring of such formulations.

Although acrylic resins have the numerous possible advantages notedabove, certain intrinsic characteristics of acrylic resins have limitedtheir scope of application or have complicated their handling orreliability. Such characteristics include brittleness of cured polymers,oxygen-inhibited thin liquid layer remaining on the surface of the curedpolymer that leaves a dull surface after being wiped off, and highexothermicity accompanying the polymerization process. Although the highexothermicity is observed primarily during rapid polymerization ofunfilled or low-filled lower molecular weight acrylate monomers, suchcompositions and requirements of fast cure are considered highlydesirable in certain clinical applications. Examples of applicationsraising concern with regard to exothermic effects generated during cureof acrylic monomers include cured or cemented in situ medical and dentaldevices such as hip prostheses, dental fissure sealers, temporary orpermanent crowns and bridges and cemented orthodontic appliances.

There were several prior attempts to address the problems related to theshortcomings of acrylic resins. One such attempt was to use highmolecular weight monomethacrylate monomers. While this approacheffectively lowered the exothermic effect of the curing process, theresulting polymer was mechanically weak, brittle and theoxygen-inhibited layer was pronounced. A second attempt was to usepolyethylene glycols and/or polymeric particulate fillers as inert,nonreactive ingredients. Although polymerization occurred with noexcessive heat, the cured material was brittle and cracked easily, evenwhen exposed to weak forces. Oxygen-inhibited layer was, however,slightly reduced. A third attempt was to use inorganic particulatefillers, however, the cured material was brittle and very hard; althoughthe exothermic effect of polymerization and oxygen-inhibited layer weresignificantly reduced. Another attempt was to add phthalic acid estersand other polymers flexibilizing additives. It was found that suchadditives, although efficient when incorporated in other type polymers,were of little use in acrylic resin. In addition, concerns were raisedabout their safety when employed in dental/medical materials.

Disclosed herein are modified, chemically-, heat- or light-curableacrylate compositions and objects made of such compositions. One of theprincipal features of such compositions, in preferred embodiments, istheir temporary or permanent flexibility. (The term “temporaryflexibility” is herein defined as transient flexural characteristics ofthe material during a defined time, usually 1-5 minutes after initialcure.) Such materials also generally exhibit significant improvementover unmodified acrylic polymers in their resistance to breaking understress. In addition, the oxygen-inhibited layer after polymerization isvirtually or entirely eliminated and, if desired, so is the exothermiceffect generated during the curing process of the formulations of thisinvention.

In preferred embodiments, the compositions and objects made of suchcompositions comprise:

10-90% by weight of one or more esters of acrylic or methacrylic acidcontaining one or more acrylate or methacrylate moieties per molecule.

1-60% by weight of one or more polymers or oligomers of olefinicmonomers having four to six carbon atoms and one or two double bonds permolecule, such polymers preferably having molecular weight of 300-2500and viscosity of 25-4500 cp.

In the present specification and claims, ranges for components such asthose above mean that if there is one recited component, it is presentat a concentration within the stated range (as compared to the weight ofthe entire composition) and if there are two or more species of therecited component present, the total combined weight of all such specieswill fall within the stated range. Within the range is to be read asinclusive of the upper and lower limits.

The composition optionally comprises one or more of one or more of thefollowing compounds and/or materials: polymerization activating agents,UV absorbers, stabilizers for preventing premature polymerization,organic and/or inorganic fillers, colorants, such as pigments and/ordyes (for aesthetic, diagnostic or use-facilitating purposes), and otherdesirable additives to enhance mechanical or visual/optical propertiesof the material. Polymerization activators include, but are not limitedto, amines, preferably tertiary amines, and/or peroxides. Preferredpolymerization activators include, but are not limited to, benzoylperoxide, halogen substituted derivatives of benzoyl peroxide, N,Nbis-(2-hydroxyethyl) p-toluidine, N,N diethyl-p-toluidine,camphoroquinone, tertiary aliphatic amines, trialkylamines,methacroylalkyl-dialkylamines, and combinations of the foregoing. Ifpresent, the one or more polymerization activators are preferablypresent at concentrations of about 0.5-2% by weight. Stabilizersinclude, but are not limited to BHT, and, if stabilizers are present,they are preferably present at about 0.01-0.1% by weight, or insufficient quantity to prevent premature polymerization of the materialduring storage and/or transport. Preferred fillers include glass, silica(amorphous and/or fumed), quartz silica, aluminum oxide, zirconiumoxide, barium sulfate, and mixtures thereof. If present, fillerspreferably comprise about 10%-30% of the composition by weight,including about 15%-25%.

The composition may be produced and stored as a single part or it may beas two or more parts, each of which has some or all of the componentchemicals and materials of the composition. The two (or more) parts aremixed prior to application or use. Two or more part formulations arepreferred for those formulations of the composition which self-cure orchemically cure. For those compositions having two or more parts, theconstitution of the composition and the amounts of the component partsrefer to the composition following mixing, i.e. the composition as it isused. Accordingly, the individual parts may comprise varying amounts ofmaterials and may be mixed in any proportion such as from 1:20 (v/v) to20:1 (v/v), provided that the final composition is according to thedescription herein. In a preferred embodiment, the two parts (Part A andPart B) are mixed in a 1:1 (v/v) ratio by hand or static mixer.

It was unexpectedly found that the addition of such olefinic polymers toacrylic monomers results, after curing of such blends, in a polymericmaterial having desirable flexural and other mechanical properties,including resistance to impact and breakage. These characteristics madethem particularly useful in dental and medical applications. Thepresence of such olefinic monomers did not interfere with the curingprocess of the acrylic monomers regardless of whether the curing wasdone by heat, by chemical means or by light. In addition to desirablemechanical properties of the cured acrylate monomers modified which sucholefinic polymers, the surfaces of the resulting product are free, orvirtually free, of the oxygen-inhibited layer. Furthermore, theexothermic effect (high exothermicity) of polymerization is virtuallynot detectable or insignificant.

The discovery of the present compositions came as a total surprise, aspolyolefins were known only as modifiers of thermoplastic polymers andelastomers, and not for thermosetting polymers, to which categoryacrylate polymers belong. Furthermore, it was surprising to find thatsuch olefinic polymers are compatible with a large variety of acrylatemonomers and/or their blends, and are useful in a broad range of theirmolecular weights.

Blends comprising olefinic polymers or oligomers, preferably liquidpolymers having molecular weights in the range of approximately 100-700,and aliphatic or aromatic acrylate monomers were found to beparticularly advantageous in certain aspects. In some applications,methacrylic acid esters are preferred over acrylic acid ones.

The acrylate component of preferred compositions preferably comprisesabout 10-90% by weight of an acrylic monomer or a blend of acrylicmonomers, including about 50-80%, about 60-80%, about 50-70%, about60-80%, about 70-80%, and about 50-60% by weight. As used herein, acomposition comprising a monomer may be purely monomers, or it maycontain some or all of dimers, trimers or other oligomers. The acryatecomponent comprises esters of acrylic or methacrylic acid containing oneor more acrylate or methacrylate moieties per molecule. Examples ofacrylate monomers suitable for use in formulations of this inventioninclude, but are not limited to: ethylene and propylene glycoldimethacrylates, di-, tri- and polyethylene and propylene glycoldimethacrylates (including, but not limited to, di-polyethylene glycoldimethacrylate, tri-polyethylene glycol dimethacrylate, di-propyleneglycol dimethacrylate, and tri-propylene glycol dimethacrylate),tri-methylolopropane trimethacrylate, hydroxyethyl methacrylate,hydroxypropyl methacrylate, tetrahydrofurfuryl methacrylate,1,6-hexanediol dimethacrylate 7,7,9-trimethyl-4,13-dioxo-3,14-dioxa--5,12-diazahexadecane-1,16-diol dimethacrylate (commonly known asdiurethane dimethacrylate), 2,2-bis[4-(2-hydroxy-3-methacryloylpropoxy)phenyl]propane (commonly known asbis-GMA) and ethoxylated bisphenol-A-dimethacrylate (commonly known asEBA). In certain applications, the use of the following aliphaticmonomethacrylate monomers, preferably in mixtures with di- orpoly-dimethacrylates is desirable: C₁-C₁₂ alkyl methacrylates,cyclohexyl methacrylate, hydroxy-(C₂-C₄) alkyl methacrylates andglycerol methacrylates.

The olefinic component of preferred compositions preferably compriseabout 1-60% by weight of polymers or oligomers of olefinic monomershaving four to six carbon atoms, including about 1-10%, about 1-20%,about 10-20%, about 10-30%, about 1-40%, and about 10-40% by weight.Examples of suitable olefinic polymers or oligomers include variousolefinic polymers or oligomers derived from C₄-C₆ mono- orbi-unsaturated monomers, preferably those originated or derived frommonomers having four carbon atoms in their lineal chain such as butene,butadiene or methyl butadiene (isoprene). In most applicationspolybutene is preferred, being inexpensive and commercially available ina desirable range of molecular weights.

The compositions disclosed herein may be formed or molded into medicaldevices or used as a cement in a medical application, such as a bonecement in orthopedic surgical procedures. The materials may also bemolded or formed to create a prosthesis or dental restorative, or it maybe applied to a tooth and/or a dental appliance (including but notlimited to crowns, bridges, whether permanent or temporary), therebybeing used as a cement, cavity liner, varnish, sealer, veneer or a“bonding” material to fill in dental imperfections or a missing portionof a tooth. In accordance with one embodiment, there is provided amethod of performing a dental procedure, comprising obtaining a curablecomposition as disclosed herein in various embodiments; applying thecomposition to at least one surface of a tooth or dental appliance; andallowing the composition to cure. Accordingly, this disclosure alsoincludes the use of a curable composition as disclosed herein as acement, cavity liner, varnish, sealer, veneer, bonding material,prosthesis or dental restorative in the treatment of a diseased tooth(such as a tooth having a cavity or decay (caries)), broken tooth, ordiscolored tooth.

The following examples are given for better understanding of thecharacter of this invention and ways of its implementation; however,with no intention of outlining its scope, defined in the claims.

EXAMPLE 1

A heat curable composition consisted of: % (by weight) Diurethanedimethacrylate 73.58 Polybutene 9.68 BHT 0.05 Benzoyl peroxide 1.06Silica 15.63

The components were mixed and the material composition was cured in theoven at 100° C. for 1 hour. The properties of cured material are: Barcolhardness: 25-30; Flexural strength: 71 Mpa. The product was judgedsuitable for intended use, such as for a temporary crown and bridgematerial.

EXAMPLE 2

A light curable composition consisted of: % (by weight) Diurethanedimethacrylate 73.75 Polybutene 8.38 Camphoroquinone 0.26 Methacroylethyl diethylamine 0.75 Silica 16.86

The material was mixed and then cured for 20 seconds using an Optilux®dental curing device (light curing). The product was judged suitable forintended use.

EXAMPLE 3

A chemically curable composition consisted of a 1:1 (v/v) mixture ofParts A and B: % (by weight) Part A Diurethane dimethacrylate 78.96 N,Nbis(2-hydroxyethyl)-p-toluidine 0.39 Silica 20.65 Part B Diurethanedimethacrylate 73.58 Polybutene 9.68 BHT 0.05 Benzoyl peroxide 1.06Silica 15.63

The material was soft cured in 110 seconds and hard cured in 150 secondsat 23° C. (soft cure is defined as a stage at which the material becomessolid but exhibits flexibility). The properties of cured material are:Barcol hardness: 42-45; Flexural strength: 61 Mpa. The product wasjudged suitable for use.

EXAMPLE 4

A self curable composition consisted of a 1:1 (v/v) mixture of Parts Aand B: % (by weight) Part A EBA 17.29 Triethylene glycol dimethacrylate20.47 Bis-GMA 14.09 Polybutene 30.18 BHT 0.01 N,Nbis(2-hydroxyethyl)-p-toluidine 1.87 Silica 16.09 Part B EBA 18.61Triethylene glycol dimethacrylate 21.7 Bis-GMA 14.88 Polybutene 16.28BHT 0.08 Benzoyl peroxide 0.77 Silica 27.68

The material reached soft curing stage in 175 seconds and hard cured in210 seconds at 23° C. The product was judged suitable for use, but wassomewhat inferior to the product of Example 3.

EXAMPLE 5

An alternative self curable composition similar to that of Example 3 butwith different filler, consisted of a 1:1 (v/v) mixture of Parts A andB: % (by weight) Part A Diurethane dimethacrylate 53.92 N,Nbis(2-hydroxyethyl)-p-toluidine 0.38 Silica 12.97 Glass powder 32.73Part B Diurethane dimethacrylate 73.58 Polybutene 9.68 BHT 0.05 Benzoylperoxide 1.06 Silica 15.63

The cured material had similar properties to that of Example 3.

EXAMPLE 6

A chemically curable composition similar to that of Example 3, but withdifferent flexibilizing additive (polybutadiene instead of polybutene),consisted of a 1:1 (v/v) mixture of Parts A and B: % (by weight) Part ADiurethane dimethacrylate 79.09 N,N bis(2-hydroxyethyl)-p-toluidine 0.56Silica 20.35 Part B Diurethane dimethacrylate 67.03 Polybutadiene 12.21BHT 0.08 Benzoyl peroxide 1.00 Silica 19.68

The material reached soft curing stage in 85 seconds and hard cured in140 seconds at 23° C. The product was judged suitable for use.

EXAMPLE 7 (REFERENCE)

A chemically curable composition similar to that of Example 3 but notcontaining flexibilizing additive (polybutene), consisted of a 1:1 (v/v)mixture of Parts A and B: % (by weight) Part A Diurethane dimethacrylate72.77 N,N bis(2-hydroxyethyl)-p-toluidine 0.51 Silica 26.72 Part BDiurethane dimethacrylate 76.33 BHT 0.05 Benzoyl peroxide 1.15 Silica22.47

The properties of cured material are: Barcol hardness: 50-55; Flexuralstrength: 83 Mpa. The cured product was judged not suitable as atemporary crown and bridge material because of lack of flexibility.

1. A curable composition comprising: 10-90% by weight of one or moreacrylic monomers; and 1-60% by weight of an olefinic componentcomprising oligomers or polymers of one or more straight chain orbranched C₄-C₆ monomers having one or two double bonds per monomermolecule.
 2. The composition of claim 1 wherein the one or more acrylicmonomers are esters of acrylic or methacrylic acid having one to threeacrylate or methacrylate groups per molecule.
 3. The composition ofclaim 1, wherein the one or more acrylic monomers comprises (C₁-C₄)alkylene glycol dimethacrylate.
 4. The composition of claim 1, whereinthe one or more acrylic monomers comprises diurethane dimethacrylate. 5.The composition of claim 1, wherein the one or more acrylic monomerscomprises ethoxylated bis-phenol-A dimethacrylate.
 6. The composition ofclaim 1, wherein the one or more acrylic monomers comprises 2,2-bis[4-(2-hydroxy- -3-methacryloylpropoxy)phenyl]propane.
 7. The compositionof claim 1, wherein the one or more acrylic monomers comprises a hydroxy(C₂-C₄) alkyl methacrylate.
 8. The composition of claim 7, wherein thehydroxy (C₂-C₄) alkyl methacrylate, comprises hydroxyethyl,hydroxypropyl and/or hydroxybutyl methacrylate.
 9. The composition ofclaim 1, wherein the one or more acrylic monomers comprisestetrahydrofurfuryl methacrylate.
 10. The composition of claims 1,wherein the one or more acrylic monomers comprises (C₁-C₅) alkylmonomethacrylates.
 11. The composition of claim 1, wherein the olefiniccomponent comprises polybutene.
 12. The composition of claim 1 whereinthe olefinic component comprises polybutadiene.
 13. The composition ofclaim 1 wherein the olefinic component comprises isoprene.
 14. Thecomposition of claim 1, wherein the olefinic component has an averagemolecular weight of 300-2500 and viscosity of 25-4500 cp at 23° C. 15.The composition of claim 1 further comprising one or more additivesselected from the group consisting of polymerization initiators,polymerization activators, stabilizers, UV light absorbers, colorants,fillers, therapeutic agents, flavoring agents and viscosity/rheologicalmodifiers.
 16. The composition of claim 1 further comprising 1-60% byweight of one or more inorganic fillers.
 17. The composition of claim 16wherein the inorganic filler comprises glass, quartz silica, aluminumoxide, zirconium oxide, barium sulfate or mixtures thereof.
 18. Thecomposition of claim 1 wherein the composition is curable by heat. 19.The composition of claim 1, wherein the composition comprises a firstpart comprising a peroxide polymerization activator and a second partcomprising a tertiary aromatic amine polymerization activator.
 20. Thecomposition of claim 19 wherein the polymerization activator comprisesbenzoyl peroxide or its halogen substituted derivatives.
 21. Thecomposition of claim 19, wherein the tertiary aromatic amine comprisesN,N bis-(2-hydroxyethyl) p-toluidine or N,N diethyl-p-toluidine.
 22. Thecomposition of claim 19, further comprising camphoroquinone and tertiaryaliphatic amine as light-induced polymerization-activating additives.23. The composition of claim 22, wherein the amine is selected from thegroup consisting of trialkylamines, methacroylalkyl-dialkylamines, andcombinations thereof.
 24. The composition of claim 1, further comprisingcoloring agents such as pigments and dyes.
 25. The composition of claim1 wherein the composition is curable by light.
 26. A medical or dentaldevice, comprising the composition of claim
 1. 27. The medical or dentaldevice of claim 26, wherein said device is a dental restorativematerial, prosthesis, cement, cavity liner, varnish or sealer.
 28. Amethod of performing a dental procedure, comprising obtaining a curablecomposition comprising: 10-90% by weight of one or more acrylicmonomers; and 1-60% by weight of an olefinic component comprisingoligomers or polymers of one or more straight chain or branched C₄-C₆monomers having one or two double bonds per monomer molecule; applyingthe composition to at least one surface of a tooth or dental appliance;and allowing the composition to cure.
 29. The method of claim 28,wherein the allowing the composition to cure comprises applying heat tothe composition.
 30. The method of claim 28, wherein the allowing thecomposition to cure comprises applying UV or visible light to thecomposition.
 31. The method of claim 28, wherein the curable compositionis in two parts.
 32. The method of claim 31, further comprising mixingthe two parts prior to applying.
 33. The composition of claim 28 whereinthe one or more acrylic monomers are esters of acrylic or methacrylicacid having one to three acrylate or methacrylate groups per molecule.34. The composition of claim 28, wherein the one or more acrylicmonomers are selected from the group consisting of (C₁-C₄) alkyleneglycol dimethacrylate, diurethane dimethacrylate, ethoxylatedbis-phenol-A dimethacrylate, 2,2-bis [4-(2-hydroxy--3-methacryloylpropoxy)phenyl]propane, hydroxyethyl methacrylate,hydroxypropyl methacrylate, hydroxybutyl methacrylate, andtetrahydrofurfuryl methacrylate.
 35. The composition of claim 28,wherein the olefinic component comprises polybutene, polybutadiene,and/or isoprene.